The instant invention is a catalyzed process for the redistribution of linear, chloride or hydroxy end-terminated polyorganosiloxanes or cyclic polyorganosiloxanes. In an additional embodiment of the instant invention, the catalyzed redistribution process is part of a three-stage process for producing high yields of cyclic polyorganosiloxanes. Effective catalysts for the described processes are alumina, silica-alumina, activated carbon, zeolite, and acid clay.
Current industrial processes for the manufacture of silicone fluids, resins, and rubbers typically require as starting materials either hydroxy end-terminated linear polyorganosiloxanes or cyclic polyorganosiloxanes. These polysiloxanes can be produced by the hydrolysis of lower molecular weight polyorganohalosiloxanes and diorganodihalosilane. This process results in a polydispersed mixture of cyclic and linear polyorganosiloxanes. Separation of this polydispersed mixture, to isolate a desired linear or cyclic fraction, results in an excess of either linear or cyclic materials, as well as materials of undesired molecular weight. Therefore, a process which allows for converting linears to cyclics and vice-versa and allows for adjustment of molecular weight of polyorganosiloxane chains is desirable to allow recovery of these excess siloxanes.
Known methods for enhancing the production of cyclic polyorganosiloxanes include cracking of the polyorganosiloxanes, which is capital intensive; vacuum hydrolysis, which has poor enhancement capabilities; and aqueous hydrolysis, which tends to sacrifice chloride recovery. Other methods for enhancing the production of cyclic polyorganosiloxanes require the addition of solvents or surfactants, which makes recovery of the product more difficult and can compromise product purity.
There are many reports in the patent literature dealing with redistribution of polyorganosiloxanes in the presence of halosilanes or a halogen substituted siloxane and a catalyst. Sauer, U.S. Pat. No. 2,421,653, issued June 3, 1947, describes a process for effecting reaction between a hydrocarbon-substituted polysiloxane and a halosilane. The process may be run at an elevated temperature in the presence of a catalyst such as a hydrogen halide, or at room temperature in the presence of a hydrogen halide catalyst and an iron halide.
Brown, U.S. Pat. No. 3,065,252, issued Nov. 20, 1962, describes the reaction of halosilanes or halosiloxanes with organosiloxanes in the presence of catalysts, such as aminoalkyl-substituted organosilicon compounds, salts of monocarboxylic acids and aminoalkyl-substituted organosilicon compounds.
Brown, U.S. Pat. No. 3,101,361, issued Aug. 20, 1963, describes the interaction of a silane or silicone containing at least one halogenated silicon atom per molecule with a siloxane in the presence of catalysts such as aliphatic hydrocarbon amines, salts of monocarboxylic acid, and aliphatic hydrocarbon amines and an organic solvent.
Brown et al., U.S. Pat. No. 3,162,662, issued Dec. 22, 1964, describes a process for preparing linear chlorosiloxanes by reacting a halosilicon compound with cyclotrisiloxane in the presence of catalysts such as amines, amine salts of monocarboxylic acids and quaternary ammonium halides, amides, alkali metal halides, and ammonium salts of monocarboxylic acids; and inert organic solvents.
Wegehaupt et al., U.S. Pat. No. 3,549,680, issued Dec. 22, 1970, describes a process for preparing organohalogenosilicon compounds by reacting halogenosilicon compounds with organosiloxanes free of halogen bonded silicon, in the presence of phosphonitrile halides and organonitrogen derivatives of phosphorous acid or phosphoric acid.
Bennett, U.S. Pat. No. 3,642,851, issued Feb. 15, 1972, describes a process for preparing linear halosiloxane polymers through the redistribution of halosiloxanes or a halosiloxane with cyclotrisiloxane or cyclotetrasiloxane in the presence of phosphine oxides or amine oxides.
Bakassian et al., U.S. Pat. No. 3,646,088, issued Feb. 29, 1972, discloses conducting a redistribution reaction between a siloxane and a chlorosilane in the presence of hexalkylphosphotriamide.
Frey et al., U.S. Pat. No. 4,113,760, issued Sept. 12, 1978, describes a process comprising reacting a chlorosilane with organosiloxanes in the presence of activated charcoal. The organosiloxanes which were described for the process were cyclics of formula (R.sub.2 SiO).sub.n', and linear organosiloxanes of formula R.sub.3 SiO(R.sub.2 SiO).sub.m SiR.sub.3, where R represents hydrogen or the same or different monovalent hydrocarbon radicals and halogenated hydrocarbon radicals.
The present processes offer advantages over previously described processes. The present processes can be used not only to enhance the production of cyclic polyorganosiloxanes, but also to control the cyclic content from about zero to greater than 90 weight percent of the product. The described catalysts improve the rate of redistribution while minimizing organic cleavage. Cyclic polyorganosiloxanes as well as linear, chloride or hydroxy end-terminated polyorganosiloxanes can easily be redistributed to more desirable chloride-end terminated polyorganosiloxanes of 2 to 5 siloxane units. In addition, no solvents or surfactants are required and the catalyst are readily available and easily separated from polyorganosiloxane products.